Rear suspension bump steer

[Ross Nicol]

What a great little package, no wonder it's lifting a wheel. You might knock me off in the 40 Tim but You may have the same trouble as the Westfield/Beams and torque could win out.Be good fun to have a match up but I'd be wanting to do it at Sandown and you would want Winton.Have you got a 2A log book? I would be surprised if you got a 2B.
Hopefully your wife doesn't put her foot down. I feel the Europa would collapse with that power, especially in the driveline so 170hp/700kg will have to suit me in that car.
Ross

 

[Jim Cowden]

Tim to make it fair I think your wife should race Ross.
What do you think.

Jim

 

Ross, funny you should mention Winton. My brother Dave was down there on friday with a bunch of Vic elise owners. He had his N/A Honda-Elise and S/C Honda-Exige there for test drives.
He hasn't been to Winton before. He did a 1:32, not sure how that compares, but he reckons (as did those observing) that it would go under 1:30 with some practice.
Winton does sound like a good Lotus track. Hope to get there one day.

 

[Ross Nicol]

Tim I'll be racing at Winton at the end of the month so I'll get times in the 40 then.That track definately suits lotus and the guys love driving there. What did David think of it? We are a long way off topic, apologies for that Jim.
Ross

 

[Chris Duncan]

""but there was a bit of hopping going (on at the rear) whilst applying power after the apex.""

chassis flex? Still waiting for someone to independently torsion test an RF. The last time at the historics at the local track a Cobra was leading his class but he had mad hop powering in the turns. Too much flex.

so nice to see a long detailed discussion of handling and suspension. Usually it's just more HP. Now if we could just get some "dyno" handling testing like skid pad and cone time comparisons. Anybody using a G-meter?

the only problem that comes from 2 parallel links in place of a triangular lower arm is that the inboard pickup of the rear parallel link is further to the rear of optimum chassis strength. Getting back there where there's more flex, requiring more (heavy) chassis extension.

 

[Russ Noble]

the only problem that comes from 2 parallel links in place of a triangular lower arm is that the inboard pickup of the rear parallel link is further to the rear of optimum chassis strength. Getting back there where there's more flex, requiring more (heavy) chassis extension.

Not necessarily so Kalun. A lot of reverse A arms have the inner pickup point approx in line with the rear mount on the upright. In that case the second link is forward of that point.

However I take your point, if one was designing from scratch with the triangular lower arm one would use the forward mounting option and in that case the alternative twin link setup would require longer chassis.

In the case of a GT40 replica however there is the necessity to extend a structure rearwards for rear body mounts. So building this to incorporate the additional pickup points carries only a minimal weight penalty.

Good point though.

Cheers

Edit. Sorry Kalun, just re-read your post again. I agree with what you say about chassis strength and flex. In the case of existing setups with the rear mounted A arms, flex will (should) have already been addressed. So the weight penalty you are talking about is already there. So yes, you are right, there is a weight penalty with twin links AND rear mounted A arms, compared to front mount A arms!

 

[Bobski]

Hey guys,
I'm a couple of weeks away from doing my wheel alingment and was wondering if anyone can give us a heads up on a good starting point. What I'm after are as many aspects as possible for the front and the rear.
I have the standard RF rear set-up with 550lb springs up front and 400lb springs at the back. I also have Koni 8211 shocks all round. I'd loke to give the standard set up a go and when I can afford to, I'll upgrade.

Thanks
Bob

 

[Ross Nicol]

Bob Road car settings

Front
No more than 1 degree of neg camber each side
.5 to 1mm toe in each side
Caster is preset by the bushes on either side of the upper rose joints

Rear
Go to my earlier explanation on bump steer in this thread otherwise PM me. You need to get the bump steer under control before static settings are made.
Static settings
No more than 1 degree of neg camber each side
.5mm or more toe in each side depending on toe change at bump.


Bump steer
Caster changes can be made to contol bump steer.5 degrees in my case.Use a digital level (inclinometer, try saying that with a few beers on board). Hold it against the machined flat on the rear of the upright where the 2 threaded holes are.I had to change the length of my trailing arms,hope you don't have to it's a pain.
Ross

 

[Jim Cowden]

Bob

When you start pulling caster on the back you will most likly find the lower trailing link will start to rub on the chassis.
You may have to redrill the hole in the clevis (should be big enough).
Or get some with more offset.

Jim

 

[Bobski]

Thanks to Ross and Jim, both of you have put a lot of thought into this and appreciate you sharring all of your input.
I'm going to play with the standard setting and put into play what I've learned, once the car is on the road I'll share my findings and return what I've taken.
Thanks again

Bob.

 

[Russ Noble]

Bob,

You sound like you are going to start with the standard setting and go from there. Why re-invent the wheel? Ross and Jim have been there.

Why not save yourself a bit of time and use Ross' settings as your start point and play from there.

Just my two cents.

Cheers

 

[Bobski]

Sorry Russ, what I meant to say is that I'll be using Ross's setting to start with and if I'm happy I'll leave it at that, otherwise when I can afford to I'll be upgrading to Jim's set up. That I was after setting that I can use.

Bob

 

[Bobski]

That I was after setting that I can use.

Bob

That should read "Thats why I was after suspension setting that I can use."

 

hi ross. (kiwi) what wheel rates on springs and shocks are recomended for the aus, road going cars ? i can work back from there. thanks steve.

 

[ChrisL]

I thought it would be worthwhile sharing my ongoing experiences on this subject. Theory is all good-and-well but you can't beat some practical testing. So I take back all my theories that I posted earlier on this thread. To save you scrolling back to find my previous post, I worked on the theory that toe-out on bump was not so bad as long as it started with a small toe-in value and didn't toe out beyond zero degrees.

I've now modified the rear suspension so that it uses a similar geometry to Ross's and ran it for the first time on the track (at Sandown). I can state categorically that the handling characteristics are far improved on what I had previously.

It is now possible to brake far deeper into the corner and even allow the tail to hang out a bit knowing that the transition to a "loose" is far less sudden. Didn’t feel I got enough laps to fully get to know the “new” car, but even so I still managed to improve on my previous best time at Sandown by over 1 sec.